Method and device for forming a bevel on the edge of a glass lens

ABSTRACT

The present invention relates to a method and a device for forming a bevel on the edge of a glass lens using a lens-edge machining apparatus with computer numerical control. The method of the present invention comprises the following steps: scanning the bevel groove of a glass-lens opening in a selected glass rim, said scanning including the shape of the cross section and the periphery of the bevel groove; sending the data thus obtained to a control device of the lens-edge machining apparatus; scanning the bevel groove of a glass-lens machining tool in order to determine the diameter and the shape of the cross section; sending the values thus obtained to the control device of the lens-edge machining apparatus; comparing the values of the bevel groove of the lens-edge machining tool; and machining the vebel according to the data obtained if the compared values are within a first allowance range which can be predetermined, machining the bevel according to a correction value if the compared values are within a second allowance range or interrupting the bevel machining process if the compared values are not in the first nor the second allowance ranges.

The invention relates to a method for producing a bevel on the edge of aspectacle lens using a CNC-controlled spectacle-lens edge-machiningmachine.

EP 0 706 439 B1 by the same applicant describes a method and anapparatus with which changes in the bevel because of the wear to agrinding wheel used for producing the bevel can be taken intoconsideration.

During the grinding of a bevel on spectacle lenses, wear to the grindingwheel arises in the bevel groove, the wear not only leading to a slowincrease in the size of the finish-ground spectacle lenses, but also toan increase in the size of the angle of the bevel, i.e. to a flattening.The flattening of the bevel can be accepted to a certain degree as longas the spectacle lens is securely held in the bevel groove of thespectacle frame concerned. In order to achieve this, it is proposedaccording to EP 0 706 439 B1 to subject the spectacle lens, which hasbeen ground around the circumferential contour, to a correction grindingwhich takes the flattening of the bevel into consideration. For thispurpose, the spectacle-lens edge-machining machine has, adjacent to thegrinding wheel, a support having a wedging groove whose wedge anglecorresponds to a permissible, maximum angle of a bevel on the spectaclelens. If the spectacle lens, ground into shape and provided with abevel, is inserted into the wedging groove, a measured value which isexclusively dependent on the radial wear of the grinding wheel isproduced, as long as the angle of the groove of the shape-groundspectacle lens does not exceed the angle of the wedging groove on thesupport.

Until angle parity has been reached, its suffices to undertake acorrection grinding which corresponds to the linear difference inradius. If the wear to the grinding wheel used for the bevel grinding isso great that the angle of the ridge bevel is greater than the angle ofthe wedging groove on the support, the spectacle lens to be measured canno longer enter with its ridge bevel completely into the wedging groove,so that a greater difference is measured than corresponds to the linearchange in diameter of the grinding wheel. In this case, thespectacle-lens edge-machining machine can end the grinding procedure andoutput a signal which indicates to the operator that the grinding wheelhas to be trimmed and has become unusable.

In order to ascertain whether the angle of the bevel on the shape-groundspectacle lens has exceeded a predetermined value, the support has aflat region in addition to the wedging groove, and at least one radiusvalue for the tip of the bevel in the wedging groove and a furtherradius value with regard to the flat region are recorded. It can then bedetermined from the difference in these values in comparison to adesired value whether or not the change still lies within permissiblelimits.

The method and the apparatus disclosed in EP 0 706 439 B1 have beentried and tested, but require an additional correction grinding if thereis a change to the bevel groove or to the diameter of the grinding wheelwhich requires correction. Also, it can only be ascertained that thegrinding wheel has to be trimmed and has become unusable if a spectaclelens which has already been ground into shape is being measured on thesupport. Furthermore, in the case of the known method and apparatus thecross-sectional shape of the bevel groove in the spectacle frame, forwhich the spectacle lens which is to be ground into shape is intended,is not taken into consideration during this test procedure.

The invention is therefore based on the problem of providing a methodand an apparatus for producing a bevel on the edge of a spectacle lens,using which the wear to a bevel groove in a spectacle-lensedge-machining tool is checked before the machining of the spectaclelens is carried out, and using which it is also possible to take intoconsideration the shape of the bevel groove in a selected spectacleframe.

Taking this problem as the starting point, a method for producing abevel on the edge of a spectacle lens using a CNC-controlledspectacle-lens edge-machining machine is proposed comprising, accordingto the invention, the following steps: scanning the bevel groove of aspectacle-lens opening in a selected spectacle frame, including thecross-sectional shape and the circumference of the bevel groove,inputting the determined values into a control device of thespectacle-lens edge-machining machine, scanning the spectacle-lensedge-machining tool with regard to its diameter and the shape of itsbevel groove, inputting the determined values into the control device ofthe spectacle-lens edge-machining machine, comparing the values of thecross-sectional shape of the bevel groove of the spectacle frame withthe values of the cross-sectional shape of the bevel groove of thespectacle-lens edge-machining tool, carrying out the machining of thebevel using the determined values, if the compared values of thecross-sectional shape and the diameter of the spectacle-lensedge-machining tool lie within a predeterminable first tolerance range,or carrying out the machining of the bevel using a correction value, ifthe compared values of the cross-sectional shape lie within a secondtolerance range and/or the diameter of the spectacle-lens edge-machiningtool is smaller than a predeterminable minimum value, or breaking offthe machining of the bevel, if the compared values lie outside the firstand second tolerance range.

The invention is based on the consideration that, firstly, with regardto their cross-sectional shape the bevel grooves in the spectacle framelie within a tolerance range, the cross-sectional shape of the bevelgroove being determined by the depth of the bevel groove and the angleenclosed by the flanks of the bevel groove. The depth of the bevelgroove and the flank angle and also the diameter of the spectacle-lensedge-machining tool can move within a permissible tolerance range.

Secondly, a new, unused spectacle-lens edge-machining tool has a bevelgroove which can be produced very precisely with exacting tolerances.However, during the grinding of the bevel of a spectacle lens, wear tothe spectacle-lens edge-machining tool with regard to its diameter andthe cross-sectional shape of the bevel groove arises, the wear not onlyleading to an increase in the size of the finish-ground spectacle lens,but also to an increase in the size of the angle of the bevel, i.e. to aflattening.

If a comparison between the actual state of the bevel groove in thespectacle frame and that of the bevel groove in the spectacle-lensedge-machining tool is carried out, in many cases despite wear to thebevel groove having been ascertained and possibly after undertaking acorrection during the production of the bevel, the spectacle-lensedge-machining tool can continue to be used if the cross-sectional shapeof the bevel groove in the spectacle frame permits this. In this case, areduction in the diameter of the spectacle-lens edge-machining tool canbe taken into consideration by correcting the feed motion of thespectacle lens with regard to the spectacle-lens edge-machining tool.

Since the scanning of the bevel grooves in the spectacle frame and inthe spectacle-lens edge-machining tool is carried out before thespectacle lens is machined into shape and provided with a bevel,additional correcting steps are not required, rather any correctionrequired is included by computation in the data record for theCNC-controlled machining of the spectacle-lens edge, so that thespectacle-lens edge machining directly delivers a spectacle lens whichis suitable for the selected spectacle frame, has been ground to shapeand is provided with a bevel.

The scanning of the bevel grooves in the spectacle frame and in thespectacle-lens edge-machining tool can preferably be carried out in acontactless manner by means of video-scanner systems, and thecross-sectional shape of the bevel groove can be reproduced on a viewingscreen. An apparatus for the contactless scanning of the bevel groovesin spectacle frames by means of a video-scanner system is described inDE 40 19 866 A1 by the same applicant. However, laser-scanner systemsare also suitable.

The first tolerance range, which permits the machining of the bevel tobe carried out using the determined values without including acorrection value, may cover an angular range of the bevel groove of thespectacle frame, which is equal to or greater than the angular range ofthe bevel groove of the spectacle-lens edge-machining tool, may cover adepth range of the bevel groove of the spectacle frame, which is equalto or smaller than the depth range of the bevel groove of thespectacle-lens edge-machining tool, and may cover a diameter range ofthe spectacle-lens edge-machining tool, which is equal to or smallerthan the desired diameter of the spectacle-lens edge-machining tool.

The second tolerance range, which permits the machining of the bevel tobe carried out with a correction value being included, may cover anangular range of the bevel groove of the spectacle frame, which issmaller than or equal to the angular range of the bevel groove of thespectacle-lens edge-machining tool, in which the maximum value of theangle of the bevel groove of the spectacle-lens edge-machining tool mustnot exceed a predeterminable value, and the correction value isdetermined from the depth of penetration, which can be calculated fromthe actual angles of the bevel grooves of the spectacle frame and of thespectacle-lens edge-machining tool, of the bevel on the shape-groundspectacle lens into the bevel groove of the spectacle frame, in such amanner that the spectacle lens is machined smaller by a radial valuewhich corresponds to the distance between the bevel tip on the spectaclelens and the base of the bevel groove of the spectacle frame. A furthercorrection value may, if required, be determined from the reduction indiameter of the spectacle-lens edge-machining tool.

If the compared values lie outside the first and the second tolerancerange, the machining of the bevel is broken off, specifically if itturns out that the angle and the depth of the bevel groove of thespectacle frame are greater than the angle and the depth of the bevelgroove of the spectacle-lens edge-machining tool, or if the angle of thebevel groove of the spectacle-lens edge-machining tool is greater than apredeterminable maximum value.

A spectacle-lens edge-machining machine which is suitable for solvingthe problem mentioned at the beginning can have at least onespectacle-lens edge-machining tool with a bevel groove, a rotablespectacle-lens holding shaft which is at least radially adjustablerelative to the spectacle-lens edge-machining tool, a control devicecontrolling the spectacle-lens edge-machining machine, an apparatuswhich is connected to the control device and is intended for scanningthe bevel groove of the spectacle-lens edge-machining tool with regardto diameter and cross-sectional shape and circumference, an apparatuswhich is connected to the control device and is intended for scanningthe bevel groove of a spectacle-lens opening in a selected spectacleframe, including the cross-sectional shape, a comparison device in thecontrol device for comparing the values of the cross-sectional shape ofthe bevel groove of the spectacle frame with the values of thecross-sectional shape of the bevel groove of the spectacle-lensedge-machining tool, and a device for controlling the implementing ofthe bevels using the determined values, if the compared values of thecross-sectional shapes and of the diameter of the spectacle-lensedge-machining tool lie within a predeterminable first tolerance rangeor the carrying out of the machining of the bevel using a correctionvalue, if the compared values of the cross-sectional shapes lie within asecond tolerance range and/or the diameter of the spectacle-lensedge-machining tool is smaller than a predeterminable minimum value, orthe breaking off of the machining of the bevel, if the compared valueslie outside both tolerance ranges.

The apparatuses for scanning the bevel groove in the spectacle-lensedge-machining tool and in the spectacle frame may preferably consist ofcontactless video-scanner systems, which particularly preferablycomprise CCD cameras.

These CCD cameras supply data which are digitized via animage-evaluating system in the control device and with the aid of whichthe comparison of the bevel grooves of the spectacle frame and of thespectacle-lens edge-machining tool can be carried out under computercontrol, and which enable the bevel groove of the spectacle-lensedge-machining tool and of the spectacle frame to be reproduced on aviewing screen.

However, laser-scanner systems are likewise suitable.

With the aid of the image-evaluating system and a corresponding computerprogram in the control device, it is furthermore possible for the bevelgroove of the spectacle frame and, inserted therein, a bevel of aspectacle lens, corresponding to the bevel groove of the spectacle-lensedge-machining tool, to be reproduced on the viewing screen, so that itcan be seen directly on the viewing screen whether the machining of thebevel can be carried out without inserting a correction value, with acorrection value or not at all.

However, this representation is used only for information for theoperator, since the machining of the bevel is carried out by means ofthe control device under fully automatic control in accordance with thecriteria mentioned above.

The invention is explained in greater detail in the following withreference to an exemplary embodiment illustrated in the drawing, inwhich:

FIG. 1 shows a perspective view of a spectacle-lens edge-machiningmachine according to the invention,

FIG. 2 shows a cross section through the spectacle-lens edge-grindingmachine according to FIG. 1,

FIG. 3 shows a schematic illustration of an apparatus for scanning abevel groove of a spectacle frame,

FIG. 4 shows an enlarged illustration of various bevel groove shapes ina spectacle-lens edge-machining tool,

FIG. 5 shows a cross section through a spectacle frame with variousbevel groove shapes being illustrated,

FIGS. 6 to 9 show an illustration of a spectacle lens which has beenground into shape and has a bevel made on it being fitted into aspectacle-lens opening of a spectacle frame with the formation of thebevel groove in the spectacle frame and of the bevel on the spectaclelens differing as a function of the wear to the spectacle-lensedge-machining tool.

A housing 1 of a CNC-controlled spectacle-lens edge-grinding machinewhich is known per se is illustrated, in whose grinding chamber 2 threegrinding wheels 3 are arranged on a shaft 4. One of the grinding wheels3 having a cylindrical surface is used for the preliminary grinding ofthe contour form of a spectacle lens 9, while the two other grindingwheels are used for starting to grind different ridge bevels onto thepreliminarily ground spectacle lens 9. The bevel on a grinding wheel isindicated by the reference number 11.

Arranged parallel to the shaft 4 having the grinding wheels 3 is aspectacle-lens holding shaft consisting of coaxial, rotable half-shafts5, 6, the half-shaft 6 of which can be displaced axially. At their endsthe half-shafts 5, 6 have annular holding heads 8, between which anunmachined lens 9 can be clamped. The clamping can take placeautomatically or via a handle 7.

The grinding of the circumferential edge in accordance with apredetermined shape of the spectacle lens takes place in a known mannerunder CNC control using a control device 12. The control device 12 isconnected to an input apparatus in the form of a keyboard 14 which canbe used to input the predetermined contour form, the values for bringingit out of center and, if given, the axial position of a cylindrical orprismatic grinding.

Arranged in the grinding chamber 2 is a CCD camera 10 which is connectedto the control device 12 via a converter 13. This CCD camera records animage of the bevel groove 11 in one of the grinding wheels 3, this imagebeing digitized by means of an image-processing system and beingprocessed in a computer of the control device 12.

The values input via the keyboard 14 and the bevel groove 11 recorded bythe CCD camera 10 can be reproduced on a viewing screen 15. This isexplained in detail with reference to FIGS. 4 to 9.

Reference to FIG. 2 shows that a cross slide 23 is arranged on a machineframe 31, the slide part 24 of which cross slide has guide rods 25 whichare mounted in holes 26 of projections 28 of a slide part 29 in a mannersuch that they can be displaced radially with respect to thespectacle-lens holding shaft 5, 6 with a spectacle lens 9 held by it.The slide part 29 is arranged via guide rails 30 on the machine frame 31in a manner such that it can be displaced in a direction parallel to thespectacle-lens holding shaft 5, 6 and to the shaft 4 for the grindingwheels 3.

In The shaft 4 is mounted on the slide part 24 by means of bearingsupports 16. The grinding wheels 3 and the spectacle lens 9 togetherwith their shafts 4, 5, 6 are surrounded by the housing 1 which has atrough at the bottom which is not illustrated in detail and preventscooling liquid and abrasive grit from passing into the region of thecross slide 23.

Connected to the spectacle-lens holding shaft 5, 6 is an angletransmitter which is not illustrated in detail and is connected to acomputer in the control device 12 via the converter 13.

A displacement transmitter 17 is arranged on the slide part 29 andrecords the radial displacement of the slide part 24 with respect to thespectacle-lens holding shaft 5, 6. This displacement transmitter 17 islikewise connected to the computer in the control device 12.

The radial displacement of the slide part 24 is brought about by adriving motor 18 which is activated by the control device 12 via controllines 21 and is in driving connection with the guide rods 25 via anelectromagnetic coupling 19.

Data records for the circumferential contours of the very wide range ofspectacle-lens shapes, desired values and tolerances for the bevelgroove 11 in the grinding wheel 3 and other data can be stored in amemory 20.

A spray guard 22 which engages tightly around the grinding wheels 3 andis only open in the region of contact with the spectacle lens 9 ensuresthat cooling liquid, which is supplied in the region of contact betweenthe grinding wheel 3 and the spectacle lens 9 and also abrasive grit arenot swirled around in the grinding chamber 2 in a manner such that thefunctioning of the CCD camera is impaired. The lens of the CCD camera 10can additionally be provided with an automatically opening and closingclosure flap which only opens if no grinding procedure is taking place.

While the CCD camera 10 serves to record an image of the bevel groove 11in one of the grinding wheels 3 in a computer-usable form, avideo-scanner system, which is illustrated schematically in FIG. 3, isalso provided in order to scan a bevel groove 35 in a spectacle-frameopening 34 of a spectacle frame 42. The spectacle frame 42 rests on acarrier 33, which is not illustrated in detail, and is held by means ofclamping arrangements, which are not illustrated. A holding device 36can be rotated about a rotational axis A running through the geometricalcentral point of the spectacle-frame opening 34, and above the spectacleframe 42 has an arm which is provided with a curved guide 37 whosecentral point 44 lies on the rotational axis A in the plane of thespectacle-frame opening 34. A video-scanner system 39, which preferablyconsists of a CCD camera, can be displaced within the curved guide 37 insuch a manner that in one position it lies perpendicularly above thespectacle-frame opening 34, so that its optical axis B coincides withthe rotational axis A. The video-scanner system 39 can furthermore beadjusted in the curved guide 37, so that its optical axis B forms anangle α with the rotational axis A. The video-scanner system 39 can befixed in the curved guide 37 by means of a fixing arrangement 38, forexample thumb screws. The rotable holding device 36 is provided with arotational drive 40 and is connected to an angle transmitter 41. Boththe video-scanner system 39 and the angle transmitter 41 are connectedto the control device 12, so that an image of the spectacle-frameopening 34 and the cross sectional shape of the bevel groove 35 can beshown on the viewing screen 15.

Details of the recording and evaluating of the bevel groove 35 by thevideo-scanner system 39 are described in DE 40 19 866 A1 by the sameapplicant. After scanning of the bevel groove 35 and inputting of themeasurement data into the control device 12, the correspondingspectacle-lens circumferential contour 32 of an unmachined lens clampedinto the spectacle-lens holding shaft 5, 6 can first of all be groundwith the aid of the cylindrical preliminary grinding wheel. Thecontact-pressure force occurring in the process results from the settingof the electromagnetic coupling 19 and can be set differently forspectacle lenses made of plastic or silicate glass and in accordancewith the edge thickness of the spectacle lens, which thickness isdependent on the optical values of the spectacle lens. The spectaclelens 9 is caused in a known manner to rotate by means of its shaft 5, 6,the rotational speed generally amounting to 10 to 13 rpm. An angletransmitter, which is not illustrated, transmits a pulse to the computerin the control device 12 at identical angular intervals, for example atincrements of 6° each, as a result of which the control device 12 ismade to set via the driving motor 18 the applicable radius, which is tobe ground, of the spectacle lens 9. During the grinding of thecircumferential contour 32 of the spectacle lens 9 on the preliminarygrinding wheel, the slide part 29 and therefore the grinding wheel 3 arecaused to oscillate parallel to the rotational axis of the spectaclelens 9, the said oscillating movement being changed into the oppositedirection in each case at the edge of the preliminary grinding wheel.This movement is controlled by a drive, not illustrated, for the slidepart 29 which is likewise connected to the control device 12. This driveof the slide part 29 is also used for starting to grind a bevel onto thespectacle lens 9, whose circumferential contour has been ground, bytransferring the spectacle lens 9, which has been ground into shape,into the bevel groove 11 in accordance with the three-dimensionalprofile of the bevel groove 35 in the spectacle-lens opening 34 of thespectacle frame 42, it being possible for this profile of the bevel tobe controlled by means of the control device 12.

After the spectacle-lens circumferential contour 32 has been ground bymeans of the preliminary grinding wheel in accordance with theillustration in FIG. 2, the spectacle lens 9 is automaticallytransferred onto the finish-grinding wheel having the bevel groove 11and is positioned in an exact manner with regard thereto. The spectaclelens 9 has a sufficient machining oversize for the finish grinding.

Before this finish grinding is carried out, the bevel groove 11 in thefinish-grinding wheel is compared with the bevel groove 35 in thespectacle frame 42. In order to clarify this procedure, FIG. 4illustrates a section, recorded by the CCD camera 10, of the grindingwheel 3 with the bevel groove 11 in solid lines, said bevel groovehaving a flank angle φ₁ which is smaller than the customary angle of abevel groove in a spectacle frame. This bevel groove 11 having the flankangle φ₁ corresponds to a grinding wheel 3 having a new value. Aspectacle lens whose contour has been ground to accurate dimensions cantherefore be inserted without any problem into a corresponding spectacleframe and bears with the tip of the bevel against the bevel base of thespectacle frame.

FIG. 6 illustrates this state with regard to a bevel groove 35 in aspectacle frame 42. The bevel groove 35 has an angle φ₀ which is greaterthan the angle φ₁ of the bevel groove 11 in the finish-grinding wheel 3.A radius R₁ of the spectacle lens 9 was marked in FIG. 4 and FIG. 6. Theheight of the bevel 43, i.e. the depth of the bevel groove 11 in thegrinding wheel 3, is greater than the depth of the bevel groove 35 ofthe spectacle frame 42.

FIG. 5 illustrates a cross section through a spectacle frame 42 having abevel groove 35 as has been recorded by the video-scanner systemaccording to FIG. 3. This bevel groove 35 has the flank angle φ₀ whichhas already been mentioned with regard to FIG. 6.

Over the course of time, the bevel groove in the finish-grinding wheel 3wears and first of all assumes a shape shown by dashed lines and denotedby the reference number 11 a in FIG. 4. The angle of this bevel grooveof a worn finish-grinding wheel is denoted by j₂. It can be seen that atthe same time the depth of the bevel groove 11 a has increased by theamount D₁. If a spectacle lens 9 whose contour has been ground isintroduced with a bevel 35, corresponding to FIG. 7, which has the angleφ₂, into the bevel groove 35 of the spectacle frame 42, the spectaclelens 9 having the bevel 43 a is oversized by the amount Δ₁ and has theradius R₂. By means of the comparison of the bevel groove 35 in thespectacle frame 42 with the bevel groove 11 a in the finish-grindingwheel 3, this correction value Δ₁ by which the radius R₂ has to bereduced to the radius R₁ is taken into consideration in the controldevice 12, i.e. the spectacle lens 9 is brought closer to the grindingwheel 3 having the bevel groove 11 by the amount Δ₁, so that the bevel43 a is ground in accordance with the dimensions of the bevel groove 35in the spectacle frame 42, and if the angles φ₀ and φ₂ coincide arefitted into the spectacle frame 42 in the manner illustrated in FIG. 7.

If the finish-grinding wheel 3 has been worn to so great an extent thata bevel groove 11 b having an angle φ₃ is reached, which is associatedwith an increase in the size of the depth of Δ₂, the flattened ridgebevel 43 b which has been ground with it and has the angle φ₃ can nolonger fit completely into the bevel groove 35 of the spectacle frame42, but bears with its flanks, as illustrated in FIG. 8, against theouter edges of the bevel groove 35. In this case, the bevel 43 b doesnot penetrate completely into the bevel groove 35 of the spectacle frame42 and the spectacle lens 9 having this bevel 43 b appears larger thanit actually is. The computer in the control device 12 can be programmedin the meantime in such a manner that it starts to grind the bevel 43 bonto the spectacle lens 9 with such a radius that this spectacle lenscan still be inserted into the spectacle frame 42, but in this case thebevel tip of the bevel 43 b no longer reaches the base of the bevelgroove 35 on the spectacle frame 42. The flank angle φ₃ in FIG. 4 andFIG. 8 corresponds to the permitted maximum value with regard to theflank angle φ₀ of the bevel groove 35 as is illustrated in FIG. 5.

If this angle φ₃ is exceeded, the grinding wheel is no longer suitablefor spectacle frames 42 having an angle φ₀ for the bevel groove 35. If,in the meantime, the spectacle frame 42 has a bevel groove 35 a with aflank angle φ₃, the grinding wheel can continue to be used, even if thebevel groove 11 b has a flank angle φ₃ or more. It therefore turns outthat the usability of the grinding wheel with a bevel groove does notfollow from an absolute value of the flank angle φ of the bevel groove11, but is always set in relation to the flank angle of the bevel groovein the spectacle frame, whereupon the computer in the control device 12takes a decision as to whether the bevel grinding can be carried outwith the determined data, whether it can be carried out with acorrection or whether it cannot be carried out at all.

FIG. 9 illustrates the coinciding of a bevel groove 35 a having theflank angle φ₃ in the spectacle frame 42 together with a bevel 43corresponding to the bevel groove 11 of a grinding wheel of new value.In this case, the bevel groove 35 a is so deep that the tip of the bevel43 does not touch the groove base, but the cylindrical regions of thespectacle lens 9 to the sides of the bevel 43 rest on the edges of thebevel groove 35 a. It can be seen that in such a case insertion of thespectacle lens 9 into the spectacle frame 42 is not possible, since thespectacle lens is not held securely in the bevel groove 35 a.

On the basis of the comparison of the bevel groove 35 a, recorded bymeans of the video-scanner system according to FIG. 3, in the spectacleframe 42 with the bevel groove 11, recorded by means of the CCD camera10, in the finish-grinding wheel, the control device decides prior tothe shape and bevel grinding of the spectacle lens 9 that the machiningis not possible and outputs a corresponding signal.

It therefore turns out that the machining of the bevel without taking acorrection value into consideration is only carried out if the comparedvalues lie within a predeterminable first tolerance range which coversan angular range of the spectacle-frame bevel groove 35, which is equalto or greater than the angular range of the bevel groove 11 of thespectacle-lens edge-machining tool 3, and covers a depth range of thespectacle-frame bevel groove 35 which is equal to or smaller than thedepth range of the bevel groove 11 of the spectacle-lens edge-machiningtool 3.

The machining of the bevel with inclusion of a correction value is onlycarried out if the compared values lie within a second tolerance range,the second tolerance range covering an angular range of the bevel groove35 of the spectacle frame 42, which is smaller than or equal to theangular range of the bevel groove 11 of the spectacle-lensedge-machining tool 3, in which the maximum value of the angle of thebevel groove 11 of the spectacle-lens edge-machining tool 3 must notexceed a predeterminable value, and the radial correction value isdetermined from the depth of penetration, which can be calculated fromthe actual angles of the bevel grooves 11, 35 of the spectacle-lensedge-machining tool 3 and of the spectacle frame 42, of the bevel 43 onthe shape-ground spectacle lens 9 into the bevel groove 35 of thespectacle frame 42 in such a manner that the spectacle lens 9 ismachined smaller by a radial value Δ which corresponds to the distancebetween the bevel tip on the spectacle lens 9 and the base of the bevelgroove 35 of the spectacle frame 42. A further radial correction valueis also taken, into consideration if the mean value of thespectacle-lens edge-machining tool is smaller than a predeterminableminimum value.

In contrast, the machining of the bevel is not carried out at all if itturns out that the angle and the depth of the bevel groove 35 of thespectacle frame 42 are greater than the angle and the depth of the bevelgroove 11 of the spectacle-lens edge-machining tool 3, or if the angleof the bevel groove 11 of the spectacle-lens edge-machining tool 3 isgreater than a predeterminable maximum value.

This means that the spectacle lens 9 which has been ground into shapeand provided with a bevel 43, can always be inserted in a preciselyfitting manner into a spectacle frame 42 if the control device 12decides that the machining of the bevel can be carried out. A correctiongrinding is not required for this, since any corrections which arerequired are included from the outset in the computer program forcontrolling the grinding of the spectacle lens.

The exemplary embodiment which has been illustrated and describedrelates to a video-scanner system with a CCD camera, however it is notrestricted to this, but may also comprise a laser-scanner system.

What is claimed is:
 1. A method for producing a bevel on the edge of aspectacle lens using a CNC-controlled spectacle-lens edge-machiningmachine with the following steps: scanning the bevel groove of aspectacle-lens opening in a selected spectacle frame, including thecross-sectional shape and the circumference of the bevel groove,inputting the determined values into a control device of thespectacle-lens edge-machining machine, scanning the spectacle-lensedge-machining tool with regard to its diameter and the shape of itsbevel groove, inputting the determined values into the control device ofthe spectacle-lens edge-machining machine, comparing the values of thecross-sectional shape of the bevel groove of the spectacle frame withthe values of the cross-sectional shape of the bevel groove of thespectacle-lens edge-machining tool, carrying out the machining of thebevel using the determined values, if the compared values of thecross-sectional shapes and the diameter of the spectacle-lensedge-machining tool lie within a predeterminable first tolerance range,or carrying out the machining of the bevel using a correction value, ifthe compared values of the cross-sectional shapes satisfy at least oneof lying within a second tolerance range and the diameter of thespectacle-lens edge-machining tool is smaller than a predeterminable,minimum value, or not carrying out the machining of the bevel, if thecompared values of the cross-sectional shapes lie outside the first andsecond tolerance range.
 2. The method as claimed in claim 1, in whichthe scanning of the bevel grooves in the spectacle frame and in thespectacle-lens edge-machining tool is carried out in a contactlessmanner by means of video-scanner systems, and the cross-sectional shapeof the bevel grooves is reproduced on a viewing screen.
 3. The method asclaimed in claim 1, in which the scanning of the bevel grooves in thespectacle frame and in the spectacle-lens edge-machining tool is carriedout in a contactless manner by means of laser-scanner systems, and thecross-sectional shape of the bevel grooves is reproduced on a viewingscreen.
 4. The method as claimed in claim 1, 2 or 3, in which the firsttolerance range covers an angular range of the spectacle-frame bevelgroove, which is equal to or greater than the angular range of the bevelgroove of the spectacle-lens edge-machining tool, and covers a depthrange of the spectacle-frame bevel groove, which is equal to or smallerthan the depth range of the bevel groove of the spectacle-lensedge-machining tool.
 5. The method as claimed in claim 1, 2, 3 or 4, inwhich the second tolerance range covers an angular range of the bevelgroove of the spectacle frame, which is smaller than or equal to theangular range of the bevel groove of the spectacle-lens edge-machiningtool, in which the maximum value of an angle of the bevel groove of thespectacle-lens edge-machining tool must not exceed a predeterminablevalue, and the correction value is determined from a depth ofpenetration, which can be calculated from the actual angles of the bevelgrooves of the spectacle frame and of the spectacle-lens edge-machiningtool, of the bevel on the shape-ground spectacle lens into the bevelgroove of the spectacle frame, in such a manner that the spectacle lensis machined smaller by a radial value which corresponds to the distancebetween the bevel tip on the spectacle lens and the base of the bevelgroove of the spectacle frame.
 6. The method as claimed in claim 1, 2,3, 4 or 5, in which the machining of the bevel is not carried out if itturns out that the angle and the depth of the bevel groove of thespectacle frame are greater than the angle and the depth of the bevelgroove of the spectacle-lens edge-machining tool, or if the angle of thebevel groove of the spectacle-lens edge-machining tool is greater than apredeterminable maximum value.
 7. A spectacle-lens edge-machiningmachine, having at least one spectacle-lens edge-machining tool (3) witha bevel groove (11), a rotable spectacle-lens holding shaft (5, 6) whichis at least radially adjustable relative to the spectacle-lensedge-machining tool (3), a control device (12) controlling thespectacle-lens edge-machining machine, an apparatus (10) which isconnected to the control device (12) and is intended for scanning thespectacle-lens edge-machining tool (3) with regard to its diameter andthe cross-sectional shape of its bevel groove, an apparatus (39) whichis connected to the control device (12) and is intended for scanning thebevel groove (35) of a spectacle-lens opening (34) in a selectedspectacle frame (42), including the cross-sectional shape, a comparisondevice in the control device (12) for comparing the values of thecross-sectional shape of the bevel groove (35) of the spectacle frame(42) with the values of the cross-sectional shape of the bevel groove(11) of the spectacle-lens edge-machining tool (3), and devices forcontrolling the carrying out of the machining of the bevel using thedetermined values wherein, if the compared values lie within apredeterminable first tolerance range, or the devices carry out themachining of the bevel using a correction value, and if the comparedvalues satisfy at least one of lying within a second tolerance range andthe diameter of the spectacle-lens edge-machining tool is smaller than apredeterminable minimum value, or the devices not carrying out themachining of the bevel, if the compared values lie outside bothtolerance ranges.
 8. The spectacle-lens edge-machining machine asclaimed in claim 7, in which contactless video-scanner systems (10; 39)are provided for scanning the bevel groove (11) in the spectacle-lensedge-machining tool and the bevel groove (35) in the spectacle frame(42).
 9. The spectacle-lens edge-machining machine as claimed in claim8, in which the video-scanner systems (10; 39) comprise CCD cameras. 10.The spectacle-lens edge-machining machine as claimed in claim 9, inwhich the control device (12) includes an image-evaluating system usingwhich the bevel groove (35) of the spectacle frame and, insertedtherein, a bevel (43) of a spectacle lens (9), corresponding to thebevel groove (11) of the spectacle-lens edge-machining tool (3), can bereproduced on the viewing screen (15).
 11. The spectacle-lensedge-machining machine as claimed in claim 7 or 8, in which the controldevice (12) includes a viewing screen (15) on which, via animage-evaluating system, the bevel groove (11) of the spectacle-lensedge-machining tool (3) and the bevel groove (35) of the spectacle frame(42) are reproduced.
 12. The spectacle-lens edge-grinding machine asclaimed in claim 7, in which contactless laser-scanner systems (10; 39)are provided for scanning the bevel groove (11) in the spectacle-lensedge-machining tool and the bevel groove (35) in the spectacle frame(42).